I'm not sure why you saw my want for 4k visuals in the single player, visual, story based games I prefer to play, as an opportunity to attack me personally. Perhaps read the rules or go back to Reddit or wherever that attitude is welcome.
Though they could have done 4K UI / other apps like an Android TV device I suppose.
From a consumer perspective, people have been rocking 4K TVs and 4K PCs for a few years, and even consoles have been outputting 4K (even if they're rendering less) for a while, so one would hope to have seen some sort of 4K offering.
I can see discussions on the Steam forums as far back as 2016 of people streaming 4K in-home from PC to HTPC or similar, so it's certainly _possible_, even 4-5 years ago.
I've done some 4K streaming from my gaming PC to laptop hooked up to TV in living room in the past without any (more) issues than I usually have being a purely Linux gamer.
According to a topic near the top of the Raspberry Pi / Steam Link, Steam Forum, 4K is _possible_ (no indication of what it looks/feels like) with a Pi 4B these days.